[SR-11666] URL.lastPathComponent.prefix(N) crashes if N is the exact length of the last path component string

[swift-ci]

Previous ID	SR-11666
Radar	None
Original Reporter	bryanpierce (JIRA User)
Type	Bug

Environment

macOS 10.14.6 Build tools from Xcode 11.1 uname -mprsv Darwin 18.7.0 Darwin Kernel Version 18.7.0: Tue Aug 20 16:57:14 PDT 2019; root:xnu-4903.271.2\~2/RELEASE_X86_64 x86_64 i386 swiftc --version Apple Swift version 5.1 (swiftlang-1100.0.270.13 clang-1100.0.33.7) Target: x86_64-apple-darwin18.7.0

Additional Detail from JIRA

| | | |------------------|-----------------| |Votes | 0 | |Component/s | Compiler | |Labels | Bug | |Assignee | None | |Priority | Medium | md5: 113a2b8f1574fa9e503cde77f5f0d852

Issue Description:

When calling prefix(N) on the string returned from URL.lastPathComponent an NSRangeException is thrown if the string is of length N. This only occurs when built with the -O optimization flag.

Example program:

import Foundation

let url = URL(fileURLWithPath: "/System");
let prefix = url.lastPathComponent.prefix(6)

Stack trace:

• • • Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSPathStore2 characterAtIndex:]: index (6) beyond bounds (6)'

    • First throw call stack:
      (
      0 CoreFoundation 0x00007fff50ebca7d __exceptionPreprocess + 256
      1 libobjc.A.dylib 0x00007fff7b5b7a17 objc_exception_throw + 48
      2 CoreFoundation 0x00007fff50ebc8af +[NSException raise:format:] + 201
      3 Foundation 0x00007fff5307ee50 -[NSPathStore2 characterAtIndex:] + 109
      4 libswiftCore.dylib 0x00007fff7c6fcbd3 $ss11_StringGutsV34foreignErrorCorrectedUTF16CodeUnit2ats6UInt16VSS5IndexV_tFTf4nx_n + 51
      5 libswiftCore.dylib 0x00007fff7c6fcc7e $ss11_StringGutsV18foreignScalarAlignySS5IndexVAEFTf4nx_n + 14
      6 libswiftCore.dylib 0x00007fff7c67a069 $ss11_StringGutsV18foreignScalarAlignySS5IndexVAEF + 9
      7 string-test 0x000000010006ca63 main + 323
      8 libdyld.dylib 0x00007fff7cd853d5 start + 1
      )
      libc++abi.dylib: terminating with uncaught exception of type NSException

[theblixguy]

Looks like SR-11605 which was recently fixed. cc @Catfish-Man

[Catfish-Man]

Sure does!